Power converters for medium and high voltage applications are commonly used for converting a first current at a first frequency and a first voltage into a second current at a second frequency and a second voltage. Many types of different power converters are known, such as for converting AC to AC, AC to DC, DC to AC and DC to DC.
A switching regulator is a circuit that includes a controller and a power converter. The power converter includes at least one power phase (or stage) that can comprise a power switch, an inductor, and a diode, or a high-side power transistor and a low-side power transistor connected in series between supply terminals with a converter switching node at the interconnection of the power transistors. The switching node is adapted for connection to an inductor, or 4 power switches per phase with the inductor in between for a buck-boost converter, to transfer energy from the input to the output, where the power switch(es) converts the input voltage to the desired output. The controller and power phase stage(s) are linked by a feedback loop, and the controller supervises the switching operation of the power phase(s) stage by controlling the control node(s) of the power switch(es) to regulate the output voltage to the intended voltage level.
Power Factor Correction (PFC) shapes the input current of the power supply to be synchronized with the mains voltage (line voltage input) to maximize the power drawn from the mains. In an ideal PFC circuit, the input current follows the input voltage as a pure resistor, without any input current harmonics. Although active PFC can be achieved by several converter topologies, the boost converter is the most popular topology used in PFC applications, for several reasons. The line voltage varies from zero to some peak value typically about 375 V so that a stepup (or boost) converter is needed to output a DC bus voltage such as 380 V or more. Accordingly, a buck converter cannot be used. A buck-boost converter also has a high switch voltage stress (Vin+Vout), so that it is also not a common converter choice.
The boost converter has the filter inductor on the input side of the converter, which provides a smooth continuous input current waveform as opposed to the discontinuous input current of the buck or buck-boost topology. The continuous input current is significantly easier to filter, which is a major advantage of the boost converter design because any additional filtering needed on the converter input will increase the cost and reduce the power factor due to capacitive loading of the line.